Identification cards and badges such as driver's licenses, employee identification cards, military badges, etc. are frequently made in secure manner to prevent tampering and/or counterfeiting.
European Patent Application No. 91304385.7 (Beck et al.) discloses a security laminate comprising a thermal dye transfer print, an opaque polyvinyl chloride (PVC) base sheet modified by the addition of a dye receptor layer, and a polyester cover sheet laminated over the image on the base sheet without the use of an intermediate adhesive layer. Two disadvantages of such laminates are that they require an additional dye receptor layer on the base sheet and tend to warp on cooling after lamination because the thermal expansion coefficients of the PVC base layer, which melts as the card is laminated, and the polyester cover are different.
U.S. Pat. No. 5,060,981 (Fossum et al.) discloses a transparent polyester overlay with a polymeric image-receiving layer over a hot-melt adhesive layer. Following imaging, the overlay is laminated to a substrate. A disadvantage of this approach also is that under some conditions of manufacture the card may tend to warp on cooling after lamination because of the differences in the thermal expansion coefficients of the base layer, which typically is paper, and the polyester cover layer.
Another known approach is to use a polyolefin core layer enclosed and sealed via heat lamination in an envelope of clear polyester film. This eliminates the differences in thermal expansion coefficient that lead to warpage, but requires multiple printing steps to provide information on both front and back sides.
Despite the variety of known security card constructions and known methods for producing such cards, there exists a need for improved security cards that are made by an easy, inexpensive process using inexpensive materials.